As a carbon nano tube is excellent in electric conductivity, surface area, and hydrogen storage, it is desirable to be used as a catalyst supporter, particularly as an electrode of a fuel cell. However, until now, researches on carbon nano tube have been performed mainly on its composition. Its applications made little progress and especially, there have been little attempts to utilize the carbon nano tube as a catalyst supporter. The carbon nano tube has a strong point that it can prevent the cohesion of particles when supporting metal particles due to the particular surface structure.
The platinum-based catalyst is a precious metal and is commonly used in hydrogenations and reforming reactions and has problems of high manufacturing cost in spite of the high activity compared to other metal catalysts.
Therefore, in order to solve these problems, it is important to maximize the number of the catalyst activity point using the minimum amount of platinum by minimizing the size of the platinum particle in a catalyst active state and supporting in high dispersion state. In order to do this, the surface area of the supporter which supports the catalyst should be excellent and the catalyst particle should not condense on the surface of the supporter during the supporting process.
At present, during the electrode manufacturing process, various carbon materials are used as a support of the platinum-based catalyst, there has been few cases that used carbon nano tube until now. In case the carbon nano tube is used as catalyst supporter for electrode of a fuel cell, due to the high electricity conductivity, hydrogen storage, and mechanical hardness, and excellent surface area, the performance of the electrode can be improved remarkably.
Also, the manufacturing process of the electrode for fuel cell in accordance with a related art adopted a “paste method” for a method for pasting the platinum-based supporting carbon catalyst on the carbon paper, there exists a weak point that the activity of the platinum-based catalyst is blocked during the process. On the other hand, in case when the carbon nano tube is grown directly on the surface of the carbon paper and supporting the platinum-based catalyst, the large surface area of the carbon nano tube can be used as it is and has an advantage that the reaction activity can be remarkably improved as all supported platinum-based catalyst particles are not blocked to be able to participate in the reaction.
The followings are references related to contents that the carbon nano tube is grown on the carbon electrode surface for being utilized as an electrode for a fuel cell.
Japanese Patent Publication No. 2004-59428A discloses a manufacturing method of a carbon nano tube electrode for being used as an electrode for a fuel cell, after scattering a metal catalyst using electrophoresis, spraying, sputtering, or CVD, composing a carbon nano tube using a CVD method which uses ethylene, carbon oxide, carbon dioxide, acetylene, and methane as a carbon source and raises temperature up to 400˜900° C., or the carbon nano tube can be composed using a plasma CVD.
PCT International Publication No. WO 2006/080702 A1 discloses a method which makes a nano compound including a carbon nano tube and applies this to the electrode for a fuel cell to improve the performance of the fuel cell remarkably. The method composes the carbon nano tube by supporting the nickel, cobalt, iron or the composition thereof to a carbon cloth or to a carbon fiber by sputtering, evaporation, CVD, or electroplating or electroless plating methods and flowing carbon sources. In here, in order to minimize a blockage area by growing nano tubes in a borough shape additionally following the surface of the nano tube grown at beginning, a DC plasma CVD method is used.
According to the Zhibin et al. in Materials Chemistry and Physics (vol. 85 (2004) P. 396), carbon nano tube is grown on the surface of a graphite disk and a platinum is supported to be used in a methanol fuel cell directly. They electrically supported an iron catalyst to surface of the graphite disk using a galvanostatic method, after growing the carbon nano tube using a CVD method, and supported the platinum particles in an electro-chemical method using a potentiostatic method. A scanning electrode microscope analysis result shows the size of the platinum particle to be 60-80 nm.
However, although there have been various attempts to utilize a carbon nano tube to an electrode for a fuel cell, there has been no example that uses a CVD method for effectively supporting platinum-based catalyst particles to the surface of the carbon nano tube in a nano scale after growing the carbon nano tube on a carbon paper directly.